In certain primary or auxiliary electrical power supplies, a group of batteries, such as lead acid batteries, are connected together in a string so as to provide power back-up, load management or an uninterruptable power supply. Such a system is used in, for example, typical telephone and communication applications. In these applications, 48 volts are required and is achieved by stringing 24, 2-volt, single-cell batteries together. Typically, multiple strings of from 6 to 12 strings of battery cells are often connected to the power supply in parallel. It can be seen that such a power supply system can include from 24 up to 144 separate battery cells. Each battery cell must be monitored either periodically or more preferably continually for its state of condition. It is also preferable that the condition of each battery be remotely indicated
Heretofore, individual cell and battery strings have been either locally or remotely monitored for cell terminal voltage. However, due to the requirement that the cells remain connected to the load at all times, and also due to associated charging systems, the cell terminal voltage has been recorded with the batteries still connected with the result that inaccurate terminal voltages are read.
Another and preferable means for determining the state of the condition of the individual cells is to obtain specific gravity readings of the electrolyte of each cell which has heretofore been done manually. Manual measurement and recordation of specific gravity is very time consuming, laborious, and also only provides an instantaneous indication of the cell's condition. Information is not known about the cell's condition during periods between readings and adverse conditions will not be detected at all if the condition returns to normal between readings. Also, electrolyte level has been individually, manually or visually checked which is also very time consuming, costly and does not give a continuous indication of the state of the electrolyte level.
Visual hydrometers and indicators do exist as does at least one combination visual, electronic remote indicating device. That device is disclosed in U.S. Pat. No. 3,954,010. Strictly visually indicating devices have two principal shortcomings. First, because they operate strictly in connection with visual observances, remote signaling is not possible and accordingly an observer must visually check each individual indicator at each battery cell in the string which is very labor intensive and time consuming. Furthermore, it is well known that indicators that work strictly in accordance with visual techniques cannot distinguish the difference between a low electrolyte level condition and both low specific gravity and low electrolyte level conditions occurring at the same time.
The remote indicating device of U.S. Patent 3,954,010 also suffers from significant shortcomings. First, although the device sends an electrical signal to a remote location, the meaning of the signal is not known. That is, the electronic signal can be due to either a low electrolyte level condition, or a low electrolyte specific gravity condition or both conditions occurring simultaneously.
Accordingly, the device does not electronically differentiate between such conditions or indicate which condition is occurring or if both conditions are occurring. The observer must then physically view the visual indicator portion of the device which defeats the remote signal objective and, as noted, the visual indicator portion does not distinguish the difference between a low electrolyte level and both low specific gravity and low electrolyte level conditions occurring simultaneously.